There are two general types of Stirling engines. In the first, the piston and displacer are mechanically linked to a rotating shaft by means of a linkage means for converting between rotary motion and reciprocating motion. The most common linkage of this type is the conventional crankshaft and connecting rod linkage means. The second type of Stirling engine is the free piston Stirling engine. The present invention is not applicable to free piston Stirling engines but is applicable to the first type as well as to other devices in which there is a need for a linkage which converts rotary motion to reciprocating motion and in which it is desired to have a selected phase relationship between two reciprocating bodies linked to a rotating shaft.
Although a variety of linkages are shown in the prior art, those which have been applied to Stirling engines include not only the conventional crank and connecting rod, but also the rhombic drive, bell cranks, cams and wobble plates.
In the Stirling engine, the purpose of the linkage means which connects the piston to the rotating shaft is to transfer energy from the moving piston to the rotating shaft. The purpose of the linkage means which connects the displacer to the rotating shaft is to reciprocate the displacer in the working fluid at the proper phase and with the proper waveform or translation characteristic in order to obtain the desired operation of the engine.